1. Field of the Invention
The present invention pertains to unique drilling fluids and a method for controlling seepage loss and lost circulation of drilling fluids into subterranean formation during drilling of boreholes in said formation. More particularly, the present invention relates to compositions and methods utilizing ground rubber elastomers derived from tire retreading (recapping) as a drilling fluid additive to reduce fluid loss into the formation.
2. Description of Related Art
Drilling fluids, also known as drilling “muds”, are generally slurries of clay solids or polymers used in the drilling of wells in the earth for the purpose of recovering hydrocarbons, gas and other fluid materials. Drilling fluids have a number of functions when carrying out drilling operations in the subterranean formation such as: lubricating the drill string, removing formation cuttings from the well counterbalancing formation pressures to prevent the inflow of gas, oil or water from permeable rocks (encountered at various levels as drilling continues), holding the cuttings in suspension in the event of a shutdown in drilling and pumping of the drilling mud, and cooling and lubricating the bit and drilling assembly. In addition, the drilling fluid make-up should contain materials which serve to control loss of whole fluid when porous and depleted zones are being penetrated.
One principle purpose of a drilling fluid, though, is to deposit a thin layer on the wall of the well bore thus preventing fluid loss to the formation. This low permeability filter cake (mud cake) is formed when the drilling fluid containing particles proportionate in size to the openings in the formation being drilled seals these corresponding openings in the formation to reduce the unwanted loss of drilling fluids to permeable formations.
A large variety of materials have been used or proposed in attempts to cure lost circulation. Generally, such materials can be divided into four types or categories: fibrous materials, flaky materials, granular materials and slurries (such as the gunk-squeeze).
When whole fluid loss reaches an intolerable level, it is traditional to add various bulk materials known as LCMs (Lost Circulation Materials) to the drilling fluid in an attempt to decrease or reduce drilling fluid loss. Such prior art lost circulation materials are selected from different groups of materials in the form of flakes (or laminated), granular, and fibrous materials. Materials commonly used are cheap wastes from other industries such as cellulose fiber materials. These materials can include fibrous, flake, and/or granular ground forms, and combinations thereof. Representative of such cellulose fibers include nut and seed shells or hulls including: pecan, almond, walnut, peach, brazil, coconut, peanut, sunflower, flax, cocoa bean, cottonseed, rice, linseed, oat, and the like. See for example, Gockel, U.S. Pat. No. 4,498,995, Forrest, U.S. Pat. No. 5,706,592 and Mayeux, et al., U.S. Pat. No. 5,861,362.
Additionally, other LCMs have been utilized to reduce drilling fluid outflow and gas and fluid inflow info the bore hole such as oat hulls, ground corn cobs, hydrophobic organophilic wafer wettable cotton, ground citrus pulp, ground rice bulls and ground cotton burrs. See House, et al., U.S. Pat. No. 5,071,575 and Cowen, et al., U.S. Pat. No. 5,076,944.
Furthermore a varied group of particles has been discussed as possible drilling fluid additives consisting of resilient graphitic carbon particles, lignites, leonardites, lignin-based powders, bitumens, asphalts, clays cellulosic polymers, metal silicates, starches, guar gum, cellulosic fibers, fatty acids, welan gum, hydrocarbon resins, barite, hematite, chlorides, bromides, polyphosphates, zinc, gilsonite, graphite, graphitic carbon, coke and mixtures thereof. See Green, U.S. Pat. No. 6,825,152, Zaleski, et al., U.S. Pat. No. 5,826,689 and Whitfill, et al., U.S. Pat. No. 8,043,997, a group consisting of silicate, siliconate and mixtures thereof. See Whitfill, et al., U.S. Pat. No. 6,889,780, and hardenable composition slurry comprising of diatomaceous earth, a suspending agent, lime, loss control material sodium silicate, and sulfate has been described by Verret, U.S. Pat. No. &, 7,405,182.
Indeed Several different polymers and resins in combination with various particulate materials have been discussed by Verret, U.S. Pat. No. 7,297,862, Wood, U.S. Pat. No. 8,518,224, Chatterji, et al., U.S. Pat. No. 6,802,002, Shaarpour, U.S. Pat. No. 7,088,385, Reddy, et al., U.S. Pat. No. 7,284,611, Reddy, et al., U.S. Pat. No. 7,488,705, Ghassemzadeh, U.S. Pat. No. 7,923,713, Badalamenti, et al., U.S. Pat. No. 7,717,180 and U.S. Pat. No. 866,393 and Fang, et al., U.S. Pat. No. 7,870,903.
In addition to additives, several methods for reducing drilling fluid loss have been postulated including a process using the plugging of the porous formation by means of a polymeric solution containing pseudo-emulsion spheres by Peiffer, et al., U.S. Pat. No. 4,510,988, a method for reducing lost circulation of aqueous or oil based drilling fluids wherein one or more hydrocarbon absorbent polymers are dispersed in an aqueous carrier fluid which is then injected into the lost circulation zone by Delhommer, et al. U.S. Pat. Nos. 4,633,950 and 4,704,213, and sequential injections of spacers and varied particle and fiber containing fluids all in attempts to control mud loss due to permeable formations by Ghassemzadeh, U.S. Pat. No. 8,404,622.
Most closely related to the present invention are U.S. Pat. No. 6,806,232 issued to Cart and U.S. Pat. No. 6,518,224 issued to Wood. Cart discloses a ground elastomeric crumb rubber material which is derived from re-processed used tires which are subsequently ground, screened, and separated to insure desired elastomeric rubber particle sizes. Wood, as well describes two additional ways of manufacturing crumb rubber: (1) by cryogenically freezing whole tires or tire parts and subsequently shattering the rubber in a hammer mill to break down the tire into the desired particle sizes and removing steel and fibers and (2) physically tearing apart old tires and removing unwanted steel and fibers. As opposed to the present invention, though, the previous methods for procuring functionally useful crumb rubber elastomeric particles involve the additional steps of grinding, freezing and tearing while the present invention simply collects, sods, and classifies rubber that is utilized directly from tire retreading (recapping). The present invention utilizes these rubber particle shavings (1) without further physical manipulation and (2) absent any purification process to remove steel fibers. This is an advancement in that the current invention employs a simpler, streamlined process to acquire rubber particles that is ultimately easier and more cost effective.
While if is clear that a wide array of drilling fluid additives and methods for limiting and reducing lost circulation abound, there remains an unmet need to provide an economical and functional means to stem the loss of drilling fluid through lost circulation zones in subterranean formations. The primary goat of this invention is to meet those unfulfilled needs.